Effects of metallicity on mode switching in Cepheids

Abstract

The mode switching in Cepheids is studied using the methods of the nonlinear theory of stellar pulsation, depending on the main sequence mass $M_0$ and the abundance of elements heavier than helium $Z$. The grid of evolutionary and hydrodynamic models of core--helium burning Cepheids is represented by 30 evolutionary sequences of stars with initial masses $5.7M_{\odot }\le M_0\le 7.2M_{\odot }$ and $Z=0.014$, 0.018, 0.022. For considered values of $Z$ the periods of the fundamental mode and the first overtone at the oscillation mode switching are shown to depend on the mean density of the stellar matter. The upper limit of the period of the first overtone decreases witn increasing $Z$ from $\approx 6.9$ day for $Z=0.014$ to $\approx 4.1$ day for $Z=0.022$. The theoretical period--radius relation is independent of $Z$ and agrees well (within 2.5\%) with recent measurements of Cepheid radii based on the Baade--Wesselink method. The fundamental parameters of the short--period Cepheid CG Cas were derived with application of observational estimates of the period and the rate of period change. This star is shown to be the first--overtone pulsator.

arXiv comment16 pages, 5 figures, accepted to Astronomy Letters

References in corpus (21)

• The chemical composition of the Sun
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• The Distribution of the Elements in the Galactic Disk III. A Reconsideration of Cepheids from l = 30 to 250 Degrees
• On the fine structure of the Cepheid metallicity gradient in the Galactic thin disk
• Using Cepheids to determine the galactic abundance gradient I. The solar neighbourhood
• The effect of metallicity on the Cepheid Period-Luminosity relation from a Baade-Wesselink analysis of Cepheids in the Galaxy and in the Small Magellanic Cloud
• A re-classification of Cepheids in the Gaia Data Release 2
• The Distribution of the Elements in the Galactic Disk II. Azimuthal and Radial Variation in Abundances from Cepheids
• The distance to the Galactic Centre based on Population-II Cepheids and RR Lyrae stars
• Galactic abundance gradients from Cepheids : On the iron abundance gradient around 10-12 kpc
• The PL calibration for Milky Way Cepheids and its implications for the distance scale
• The Milky Way Cepheid Leavitt law based on Gaia DR2 parallaxes of companion stars and host open cluster populations
• Observational calibration of the projection factor of Cepheids IV. Period-projection factor relation of Galactic and Magellanic Cloud Cepheids
• Cepheid distances from infrared long-baseline interferometry - II. Calibration of the Period-Radius and Period-Luminosity relations
• Using classical Cepheids to study the far side of the Milky Way disk: I. Spectroscopic classification and the metallicity gradient
• CORS Baade-Wesselink method in the Walraven photometric system: the Period-Radius and the Period-Luminosity relation of Classical Cepheids
• Galactic clusters with associated Cepheid variables. VII. Berkeley 58 and CG Cassiopeiae
• Evolution and the period-luminosity relation for red supergiants in the Magellanic Clouds
• Calibrating the Galactic Cepheid Period-Luminosity relation from the maximum-likelihood technique
• On period distribution of RR Lyr type variables in the globular cluster M3
• Evolutionary and hydrodynamic models of short--period Cepheids